Table of Contents

What is a Soil Series?

A soil series is the fundamental unit of soil classification in the United States and many other countries; it represents a class of soils with similar physical and chemical properties throughout its profile. This similarity allows for consistent management practices to be applied, predicting crop yields, and understanding the ecological role of the soil within a given landscape.

Understanding Soil Series: The Foundation of Soil Science

Soil, far from being a homogenous inert material, is a complex and dynamic ecosystem. To understand and manage this vital resource effectively, soil scientists have developed intricate classification systems. At the heart of this system lies the soil series. A soil series represents a group of soils that share a narrow range of characteristics, allowing for detailed mapping, precise management recommendations, and accurate predictions about soil behavior.

The concept of a soil series is rooted in the understanding that soils develop through the interaction of five key soil-forming factors: climate, organisms, relief (topography), parent material, and time. Variations in these factors lead to the development of different soil profiles. The soil series attempts to group soils that have experienced relatively similar influences from these factors, resulting in remarkably similar properties.

Identifying Key Characteristics

The identification of a soil series relies on carefully examining the soil profile. This involves digging a pit or using a soil auger to expose the different layers, known as soil horizons, that make up the soil from the surface down to the parent material. Soil scientists analyze numerous properties within each horizon, including:

Texture: The proportion of sand, silt, and clay particles.
Structure: The arrangement of soil particles into aggregates (peds).
Color: A strong indicator of mineral composition, organic matter content, and drainage.
pH: A measure of soil acidity or alkalinity.
Organic Matter Content: The amount of decomposed plant and animal residues.
Drainage: The rate at which water moves through the soil.
Presence of Specific Horizons: The distinct layers that have formed due to various soil-forming processes (e.g., accumulation of clay, iron oxides, or organic matter).
Cation Exchange Capacity (CEC): The soil’s ability to retain nutrients.
Mineralogy: The types of minerals present in the soil.

By comparing these properties across different soil profiles, soil scientists can determine if they belong to the same soil series. A detailed description of these properties for each series is documented in the Soil Survey Manual and associated online databases.

The Importance of Soil Series in Agriculture and Land Management

Understanding soil series is crucial for a wide range of applications, particularly in agriculture and land management. Knowledge of the specific soil series present in a field allows farmers to:

Select appropriate crops: Different soil series have varying drainage, nutrient availability, and water-holding capacity, making them more suitable for some crops than others.
Optimize fertilizer application: Knowing the soil’s nutrient status and CEC allows for precise fertilizer application, minimizing environmental impacts and maximizing crop yields.
Implement effective irrigation strategies: The water-holding capacity of the soil series determines how frequently and how much irrigation is needed.
Choose appropriate tillage practices: The soil’s structure and drainage characteristics influence the best tillage methods to use.
Predict crop yields: Soil series are often correlated with specific yield potentials for different crops.
Manage soil erosion: Some soil series are more susceptible to erosion than others, requiring specific conservation practices.

Beyond agriculture, soil series information is also essential for:

Land use planning: Understanding the suitability of different soil series for various uses, such as residential development, industrial sites, or recreational areas.
Environmental protection: Identifying soil series that are vulnerable to pollution or degradation, allowing for targeted conservation efforts.
Wetland delineation: Determining the boundaries of wetlands based on specific soil characteristics.
Construction: Assessing the load-bearing capacity and drainage characteristics of soils for building foundations.

FAQs About Soil Series

What is the difference between a soil series and a soil type?

The term soil type is an older, less precise term that was used before the modern soil classification system was developed. It generally referred to broad categories of soils based on their parent material and general characteristics. The soil series is a much more specific and well-defined classification unit, based on detailed analysis of soil profile properties. Think of soil type as a broad genus and a soil series as a specific species within that genus.

How many soil series are there in the United States?

There are thousands of recognized soil series in the United States, with new series being identified and established regularly as soil surveys continue. The exact number fluctuates, but it’s safe to say there are several tens of thousands. Each series is named, typically after a geographic location near where it was first described.

How can I find out what soil series are present on my property?

The easiest way to find out the soil series on your property is to use the Web Soil Survey (WSS), a free online tool provided by the USDA Natural Resources Conservation Service (NRCS). You can access the WSS website, delineate your area of interest on an aerial map, and generate a soil map and report that identifies the soil series present. Local NRCS offices can also provide assistance.

What is a soil phase, and how does it relate to a soil series?

A soil phase is a subdivision of a soil series, further defining the soil based on characteristics that affect its use and management. These characteristics might include slope, stoniness, degree of erosion, or surface texture. For example, a “Miami silt loam, 2 to 6 percent slopes” is a phase of the Miami soil series. The phase adds practical information for land management.

What does the name of a soil series usually mean?

The name of a soil series typically reflects a geographic feature (town, river, mountain) near where the soil was first described and mapped. For instance, the “Miami” soil series was named after Miami, Ohio, where it was initially characterized. The name provides a convenient way to reference and identify a specific set of soil properties.

What happens when a soil series doesn’t fit the established criteria perfectly?

Soil surveys often encounter soils that are similar to an established soil series but have some slight variations. These variations are often described as taxadjuncts. Taxadjuncts are mapped and managed similarly to the established series but are recognized as having slightly different characteristics. Over time, sufficient distinct taxadjuncts might lead to the definition of a new soil series.

How does the classification of a soil series impact property values?

While the soil series itself doesn’t directly determine property value, it contributes significantly. The suitability of the soil for various uses (agriculture, building, etc.) is a key factor in determining the value of the land. Soils that are well-drained, fertile, and have good structural properties are generally more valuable than soils that are poorly drained, infertile, or highly erodible.

How often are soil series updated or revised?

The descriptions and classifications of soil series are continuously updated and revised as new information becomes available and as our understanding of soil science improves. This is an ongoing process that ensures the accuracy and relevance of soil surveys. Revisions might involve changes to the series description, the creation of new series, or the reclassification of existing series.

How are soil series used in environmental modeling?

Soil series data are critical inputs for many environmental models that predict water runoff, nutrient leaching, and other environmental processes. The soil properties associated with each series (texture, drainage, organic matter, etc.) influence how water and nutrients move through the soil profile. This information is used to assess the environmental impacts of different land management practices and to develop strategies for protecting water quality and preventing soil erosion.

What are the major limitations of using soil series information?

While soil series information is incredibly valuable, it’s important to recognize its limitations. Soil maps are created at a specific scale, and the actual soil conditions on the ground can vary within a mapped area. Additionally, soil maps are based on interpretations and generalizations, and there may be some degree of uncertainty in the classification. Localized disturbances (e.g., construction activities) can also alter the soil profile and affect its properties. Therefore, it’s always recommended to conduct site-specific soil investigations when making critical land management decisions.

Can soil series change over time?

Yes, soil series can change over long periods due to natural processes like erosion, deposition, and weathering. Human activities, such as intensive agriculture, deforestation, and urbanization, can also significantly alter soil properties and lead to changes in soil classification. While dramatic changes are rare, gradual shifts in soil characteristics can occur over decades or centuries.

How are soil series related to the Soil Taxonomy system?

Soil Taxonomy is a hierarchical system of soil classification with six levels: Order, Suborder, Great Group, Subgroup, Family, and Series. The soil series is the most specific level of classification. Each soil series belongs to a specific family, subgroup, great group, suborder, and order within the Soil Taxonomy system. This hierarchical structure provides a framework for understanding the relationships between different soils and for organizing soil information.